1. Field of the Invention
The present invention relates to a hoisting apparatus for load such as luminaires used at high elevations, and particularly a hoisting apparatus characterized in that a descending position of the load can be readily and safely adjusted to facilitate maintenance works of the load.
2. Disclosure of the Prior Art
In high-ceilinged structures such as concert hall, gymnasium, and convention hall, a hoisting apparatus for luminaire has been utilized to readily perform maintenance works of the luminaire operated in the vicinity of the ceiling. The hoisting apparatus is mainly composed of a hoisting part for supporting the luminaire, drive unit for moving the hoisting part up and down by use of cable(s), and a base secured to the ceiling, on which the drive unit is mounted.
In this kind of the hoisting apparatus, when the hoisting apparatus is mounted to the ceiling of the structure, an optimum length of the cable is usually determined according to the height of the ceiling. Thereby, the hoisting part can be moved up and down between a top position where the luminaire is operated, and a bottom position where the maintenance of the luminaire is performed.
However, when it is needed to change the bottom position of the hoisting part for layout change after the optimum length of the cable is determined once, an operation of changing or adjusting the length of the cable must be performed at the ceiling again. It is impractical to often perform such a bother operation at high elevations. On the other hand, when the operation is not performed, there are problems that the maintenance works of the luminaire can not be safely performed, and the maintenance efficiency lowers.
From the above viewpoints, a primary object of the present invention is to provide a hoisting apparatus for load characterized in that the length of cable(s) can be readily adjusted such that a descending position of the load matches a position adequate for maintenance works of the load without dangerous operations at high elevations, to thereby facilitate the maintenance works of the load under the safe working condition.
That is, the hoisting apparatus comprises at least one cable, a load holder for holding the load, a base secured to a ceiling, and coupled to the load holder through the cable, and a drive unit for moving the load holder up and down by use of the cable between a top position where the load holder is located adjacent to the base and a bottom position where the load holder is spaced from the base by a distance. In the present invention the load holder has a cable-length adjust unit for adjusting a length of the cable to stop the load holder at a desired position between the top and bottom positions.
It is preferred that one end of the cable is connected to the load holder, and the opposite end of the cable is connected to the drive unit mounted to the base.
It is preferred that the cable is composed of a pair of strip cables. In this case, it is also preferred that the strip cables mutually extend in a substantially same plane.
It is preferred that the cable-length adjust unit is provided with a winding shaft rotatably supported in the load holder and a rotation-inhibiting member for inhibiting the rotation of the winding shaft, and one end of the cable is connected to the winding shaft, so that a desired amount of the cable can be wound on the winding shaft. In this case, it is preferred that the winding shaft is formed with an operation part, which is accessible from outside of the load holder to adjust a winding amount of the cable on the winding shaft, and an engagement part, to which the rotation-inhibiting member can be engaged to prevent unwinding of the cable from the winding shaft. In addition, it is particularly preferred that the winding shaft can be divided into a pair of elongate pieces along its axial direction, and one end of the cable is caught between the elongate pieces.
It is preferred that the drive unit is mounted to the base, and comprises a winding drum, to which one end of the cable is connected, and an electric motor for rotating the winding drum.
It is preferred that the base has a second cable-length adjust unit for adjusting an amount of the cable to be unwound from the winding drum. In this case, it is preferred that the second cable-length adjust unit comprises a rotating body, which is rotated at a rotation amount of less than one turn according to the rotation of the winding drum when the load holder is moved from the top position to the bottom position, and a stop switch for automatically stopping a supply of electric power to the motor when the rotating body reaches the rotation amount.
It is preferred that the rotating body is a final gear coupled to the winding drum through a reduction-gearing unit, and the final gear has a knob used to disengage the final gear from the reduction-gearing unit and change the rotation amount of the rotating body. In this case, it is also preferred that the knob of the rotating body is exposed to be accessible from outside of the base. Moreover, it is preferred that the final gear receives a spring bias in its axial direction, and is moved in the axial direction against the spring bias to disengage the final gear from the reduction-gearing unit and change the rotation amount of the rotating body.
In addition, it is preferred that the hoisting apparatus of the present invention comprises a cable receiving member provided to receive the cable at a position between the winding drum and the load holder, an elastic body for movably supporting the cable receiving member according to a change in tension of the cable, and a first switch for automatically stopping a supply of electric power to the motor when a positional displacement of the cable receiving member is caused by an elastic deformation of the elastic body according to an increase in tension of the cable. In this case, it is particularly preferred that the cable receiving member is a sheave for turning the cable unwound from the winding drum toward the load holder, the elastic body is a spring, and the supply of electric power to the motor is stopped when the sheave is displaced downward by an elastic deformation of the spring.
It is preferred that the hoisting apparatus of the present invention comprises brake unit for inhibiting a rotation of a drive shaft of the motor when the load holder is in the top position. In this case, it is particularly preferred that the brake unit comprises a pressure member of an elastic material, which is elastically deformed by the load holder when the load holder is in the top position, so that the deformed pressure member inhibits the rotation of the drive shaft of the motor by friction.
It is preferred that the hoisting apparatus of the present invention comprises a cable receiving member for turning the cable unwound from the winding drum toward the load holder, and a second switch for automatically stopping a supply of electric power to the motor when the second switch is activated by the cable itself extending between the winding drum and the cable receiving member. In this case, it is preferred that the second switch is disposed in such a position that when a slack of the cable is caused by a decrease in tension of the cable, the second switch is activated by the cable itself under the slack condition. Moreover, it is preferred that the second switch is disposed in such a position that when unwinding of the cable from the winding drum is finished, the second switch is activated by the cable itself extending between the cable receiving member and the winding drum.
In addition, it is preferred that the winding drum has a cable catching portion for catching one end of the cable, and an arcuate portion configured to enhance winding of the cable on the winding drum only when the winding drum rotates in one direction.
It is preferred that the reduction-gearing unit comprises a plurality of reduction gears engaged mutually, and a bearing unit for supporting rotation shafts of the reduction gears, and the bearing unit is provided with a plurality of projections of different heights, each of which has at its top end a concave for receiving the rotation shaft of the reduction gear, and a single supporting member, which is used only to support one of the reduction gears in cooperation with the projection of the greatest height, so that the remaining reduction gears are supported by the other projections without using an additional supporting member.
It is preferred that the drive unit comprises a winding drum, to which one end of the cable is connected, and a DC motor for rotating the winding drum, which comprises a permanent magnet and a rectifier brush. In this case, it is preferred that the hoisting apparatus of the present invention comprises a reduction-gearing unit for transmitting an output power of the DC motor to the winding drum, and the reduction-gearing unit has a self-lock mechanism for inhibiting transmission of a rotation of the winding drum to the DC motor, which is composed of a worm gear and a worm wheel.
In a preferred embodiment of the present invention, the load holder has a case for housing the cable-length adjust unit therein, which has a pair of guide projections formed such that the cable extends from the cable-length adjust unit in the case toward the base through a clearance between the guide projections, and at least one of the guide projections has a rounded tip.
In a further preferred embodiment of the present invention, the load holder is coupled to the base by use of plural cables, and has a case for housing the cable-length adjust unit therein, and the case has protrusions extending outside from its rim to prevent a situation in which the load holder suspended from the base by the cables is rotated about a horizontal axis by mistake to form a kink in the cables. In this case, it is preferred that the base has a housing with a concave into which the case is fitted when the load holder is in the top position, and each of the protrusions has an arcuate tip adapted to guide the case into the concave.
These and still other objects and advantages will become apparent from the following detail description of the invention.